Soil moisture is widely recognized as an important variable in studies related to ecology, meteorology, hydrology, agriculture and climate change. From a hydrological viewpoint, soil moisture content controls the partitioning of rainfall into runoff and infiltration, thereby affecting the runoff response in catchment areas. In recent decades, the role of soil moisture in a number of hydrological processes has been extensively studied on slope or catchment areas and has received increasing attention from the hydrological community. However, soil moisture is one of the most difficult variables to estimate because of factors such as vegetation, soil and topography. Accurate estimation of spatial and temporal variation in soil moisture is therefore required to improve both the predictive capabilities of runoff models as well as to validate representations of hydrological processes. Datasets of observed in situ moisture measurements are crucial. Unfortunately, measured soil moisture time series are not widely available and therefore simulated soil moisture series are used. We apply and test a simple parametric water balance model to simulating soil moisture conditions in different forest types (natural secondary forest, evergreen needleleaf and deciduous/coniferous plantation forest) in semiarid regions of southwestern Beijing, China. Model calibration and validation were performed using a dataset comprising averaged soil moisture content measured at depths of 0-75 cm in the growing seasons of 2006, 2007, and 2010. The models performed reasonably well in simulating the patterns and magnitudes of daily average soil moisture content in the upper 75 cm soil layer in all three forest types. Using different parameters in the model did not significantly alter the results and the model structure exhibited a relatively small amount of uncertainty. Sensitivity analysis revealed that four parameters (W_max (the maximum water capacity of the soil layer), m (a parameter linked to the non-linearity of the infiltration process), Ks (the field-saturated hydraulic conductivity), λ (the pore size distribution index linked to the structure of soil layers)) played important roles in rainfall infiltration, deep percolation and evaporative processes. In addition, differences in soil moisture flux among forest types suggested that both annual evapotranspiration in deciduous/coniferous forest plantations and infiltration in deciduous broad-leaved forest were greater than those in other forestlands;in addition, deep percolation in all three forestlands was low. We demonstrate that a simple, robust, parametric model is capable of simulating the temporal dynamics of soil moisture content in different forest types. The study of soil moisture in forest plantations in semiarid regions helps researchers clearly recognize the fundamental role of the soil-atmosphere-vegetation continuum. In addition, it provides a theoretical basis for selecting forest plantation species. It also aids the selection and design of studies that analyze the ecohydrological effects of plantations in semiarid regions. Moreover, due to its simple structure and good performance the proposed model may be incorporated in continuous-time rainfall runoff models. Similar thorough investigations should also be conducted in other basins.